Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $134.27   9.671%   $147.2553   $147.26   $147.25   $147.30  
  Purchase #2 $24.96   5.280%   $26.2779   $26.28   $26.30   $26.30  
  Purchase #3 $44.65   4.795%   $46.791   $46.79   $46.80   $46.80  
  Purchase #4 $152.40   9.843%   $167.4007   $167.40   $167.40   $167.40  
  Purchase #5 $226.80   13.793%   $258.0825   $258.08   $258.10   $258.10  
  Purchase #6 $164.64   13.312%   $186.5569   $186.56   $186.55   $186.60  
  Purchase #7 $31.92   3.637%   $33.0809   $33.08   $33.10   $33.10  
  7 purchase totals = $779.64       $865.4452   $865.45   $865.50   $865.60